A recap: Wonder Woman is taking down the members of the Justice League so that she can fight a dragon alone, because a prophecy foretold that whoever fought the dragon would beat her - but also die. So being selfless, Diana gets her team members out of the way so that she will be the only one to die. It pains her to put them in danger and betray their trust, but she strongly believes that the world is better off without her, rather than without the rest of the League. She loves her team - her family - that much. Enough that she sucker-punched Superman.
Also, I believe Diana and Superman are equal in combat ability when their powers are included. Although the scans above say that Diana doesn’t think she can beat Superman in combat, I think it’s more apt to say that she can’t beat him and then have the strength left over to fight the dragon. Honestly, a Wonder Woman/Superman fight would last a long time.
I’ll also post the battle between Wondy and the dragon, because it’s a really good one, too.